Turbo codes and low density parity-check (LDPC) codes have been introduced into a number of recent digital communications standards, including the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) technical standards, which may be relevant for a fourth-generation long-term evolution roadmap. Specifically, the 3GPP LTE technical standards specify a rate R=⅓ turbo code using two eight-state constituent component codes.
Following the success of turbo codes, iterative information processing has subsequently been applied to interference cancellation, multiple access joint decoding, and so forth. Usually, in such communications systems, soft information produced by an error control decoder may be used to partially cancel interference created by multiple access and permit a new decoding step with improved performance. Under certain conditions, the iterative exchange of soft information between the error cancellation device and the soft-output error control decoder leads to convergence where the interference may be completely removed.
Generally, it is observed that powerful error control codes that perform well on their own in additive Gaussian channels do not work well in an iterative interference cancellation environment, while weaker error control codes may operate successfully at much higher levels of interference. However, the weaker codes are often unable to achieve the low error rates required by system specifications. The inability to achieve desired low error rates has hindered the widespread application of iterative cancellation methods.